The overview of a drug delivery system (hereinafter, referred to as DDS) using liposomes can be understood with reference to Non-Patent Document 1. Examples of a primary problem of the DDS using liposomes can include low efficiency of administration of drugs charged within liposomes. Examples of one approach to solve this problem can include an approach by which tropism targeted to target cells such as cancer cells is imparted to liposomes. For example, an approach has been developed by which a liposome in which a sugar chain that specifically recognizes lectin (sugar chain-recognizing protein) is introduced in the membrane is used to control the target tropism of the liposome.
However, the approach for improving the target tropism of a liposome is an approach that focuses on the interaction between liposomes and target cells, but not an approach that focuses on the mechanism of action by which drugs charged within liposomes are transferred to target cells. Thus, the conventional approach still has the problem of low efficiency of administration of drugs charged within liposomes.
On the other hand, examples of documents that disclose the introduction of proteins into liposome membranes can include Non-Patent Documents 2 and 3. These Non-Patent Documents 2 and 3 use as a protein to be introduced, connexin that constitutes a gap junction serving as an intercellular substance transfer pathway.
Non-Patent Document 2 has disclosed that connexin 26 is synthesized in a cell-free system and then incorporated into a liposome. However, Non-Patent Document 2 has disclosed that a hemichannel, which is formed in the connexin 26-incorporated liposome, causes ascorbic acid charged within the liposome to be leaked out from the hemichannel. Hence, the liposome disclosed in Non-Patent Document 2 seems to be impossible to use in DDS using liposomes within which drugs or the like are charged.
Alternatively, Non-Patent Document 3 has disclosed that connexin 43 generated within a cell is purified and incorporated into a liposome membrane. Non-Patent Document 3 has particularly disclosed that dephosphorylation using CIP treatment after the connexin 43 incorporation into the liposome increases permeability. The phosphorylated site of connexin is present within the cell, and the treatment uses an enzyme (CIP) of 1500 or higher in molecular weight. This means that connexin is incorporated so that a site supposed to be present within a cell is positioned outside of a liposome membrane.
Attempts to introduce connexin into liposome membranes can be illustrated as described above. However, no documents have disclosed a liposome in which connexon is incorporated in a state of having a gap junction function.
Non-Patent Document 1: D. D. Lasic et al., “liposomes: from basic to applications” Elsevier Science Publishers, (1993)
Non-Patent Document 2: Ahmad S, Evans W H. “Post-translational integration and oligomerization of connexin 26 in plasma membranes and evidence of formation of membrane pores: implications for the assembly of gap junctions.” (2002) Biochem. J. 365: 693-699.
Non-Patent Document 3: Doo Yeon Kim, et al., “Gating Connexin 43 Channels Reconstituted in Lipid Vesicles by Mitogen-activated Protein Kinase Phosphorylation” (1999) J. Biol. Chem. 274 No. 9, pp. 5581-5587